Recent years have seen the development of biometric authentication technology for authenticating a user of an device or system based on a biometric image representing the user's biometric information such as a hand or finger vein pattern or a fingerprint or palm print. A biometric authentication device using such biometric authentication technology acquires, as a biometric input image, a biometric image representing, for example, the biometric information of the user who wishes to use the biometric authentication device. Then, the biometric authentication device compares the user's biometric input information represented by the biometric input image with registered biometric information, i.e., biometric information presented in a biometric image for each registered user. When the result of the comparison indicates that the biometric input information matches the registered biometric information, the biometric authentication device authenticates the user as being a legitimate registered user. The biometric authentication device then permits the authenticated user to use the device in which the biometric authentication device is incorporated or some other device connected to the biometric authentication device.
In such a biometric authentication device, biometric input information is matched with registered biometric information by, for example, extracting the feature from the biometric input information and comparing the feature with the feature extracted from the registered biometric information (see, for example, Japanese Laid-open Patent Publication No. 2007-65900, Japanese Laid-open Patent Publication No. 2001-243465 Japanese Laid-open Patent Publication No. 7-110860 and Japanese Laid-open Patent Publication No. 9-44666).
In such a known art, a fingerprint image is divided into a plurality of zones and a ridge line direction in each of the zones is extracted.
In another known art, a fingerprint image matching device divides an input fingerprint ridge line image and a registered fingerprint ridge line image into a plurality of blocks respectively, and a ridge line direction is obtained for each of the blocks. The fingerprint image matching device determines a rotational component and a translational component which provide an optimum superposition between the ridge line direction distribution in the input fingerprint ridge line image and the ridge line direction distribution in the registered fingerprint ridge line image. Then, the fingerprint image matching device carries out matching between the input fingerprint ridge line image and the registered fingerprint ridge line image which have been converted by using the rotational component and translational component.
In still another known art, a fingerprint matching method carries out matching between a registered fingerprint and an input fingerprint by comparing ridge line direction pattern and curvature pattern of the registered fingerprint with ridge line direction pattern and curvature pattern of the input fingerprint.
In still another known art, a device for classifying fingerprint patterns judges types of dermatoglyphic pattern by tracing a feature line of a dermatoglyphic pattern based on a singular minutia which is not associated with minutiae of ridges and valleys extracted from a skin image and by using the result of tracing.
The biometric authentication technology includes a so-called 1:1 authentication procedure and 1:N authentication procedure. In a 1:1 authentication procedure, together with user's biometric input information, user's identification information such as a user name or an identification number is input and thus only registered biometric information which is preregistered for the user is specified. Then the biometric authentication device matches the biometric input information only with the specified registered biometric information.
On the other hand, in a 1:N authentication procedure, user's identification information is not input to a biometric authentication device and it is difficult to specify registered biometric information corresponding to the user. For this reason, the biometric authentication device matches the biometric input information with all of the registered biometric information which is preregistered. Then, the biometric authentication device authenticates the user as a registered user corresponding to the registered biometric information which matches the most the biometric input information. Accordingly, the larger the registered biometric information, the larger the number of runs of the matching process. This inevitably takes longer time for the biometric authentication process. In particular, when a biometric authentication technology is used in a large-scale system, the number of registered user is sometimes very large. When such a large-scale system employs a server-client system, in order to carry out a biometric authentication process, accesses to a server is concentrated to increase the load of the server, which sometimes may prolong the waiting time from when the user inputs biometric information until the result of the authentication is obtained.
From the viewpoint of simplicity of use for a user, however, time for a biometric authentication process is preferably short. Therefore, a technique which limits the registered biometric information utilized for matching with biometric input information is proposed (see, for example, Japanese Laid-open Patent Publication No. 2004-145447).
In such a known art, a fingerprint matching device selects a registered fingerprint which matches the input fingerprint by comparing the value of the parameter for selection representing the feature of an input fingerprint with a parameter for selection of a plurality of registered fingerprint and matches selected registered fingerprint with the input fingerprint. As the parameters for selection, the percentage of ridge line region to the whole fingerprint region, the space between a ridge line and a valley line, the number of weighted feature points, and the values of the ridge directions at a plurality of feature points each of which ridge directions is weighted by the confidence level of the feature point.